A load switch (hereinafter referred to as “switch circuit”) used in electronic equipment or the like may be provided between a power source and a load. The switch circuit may be switched between an ON state and an OFF state. The load may be a CPU, a memory unit, a camera, an electronic device, or the like, for example.
In such a switch circuit, a MOSFET (MOS transistor) having a low ON-state resistance, but which still meets maximum device current requirements, is often used as a switching element. A source of the MOSFET is connected to a power source, and a drain of the MOSFET is connected to the load. The switch is not always operating at the maximum possible device current level, that is, there may be cases when the current level is below the maximum operating capabilities of the MOSFET switch. In such a condition, there may arise a state where a minute current flows into the MOSFET depending on an operation state of the load (that is, the impedance of the load). In such a case, when the switch circuit is switched to an OFF state from an ON state, then a source voltage and a drain voltage of the MOSFET are at a power source voltage and a gate voltage is raised from 0V to the power source voltage such that the MOSFET may be turned off (placed in an OFF state), but because an output current which flows into the load is small, it takes a relatively long time to discharge a residual charge which is stored as a parasitic capacitance between the gate and the drain of the MOSFET. Accordingly, an output voltage of the switch circuit, which is the drain voltage of the MOSFET, transiently becomes greater than the gate voltage (power source voltage) by the voltage at both ends of the parasitic capacitance and hence, the output voltage from the switch becomes larger than the power source voltage during the transition period after switching states are changed. Accordingly, there exists a possibility that the load is erroneously operated because the output voltage temporarily exceeds the power source voltage.